1 //===-- StackMapLivenessAnalysis.cpp - StackMap live Out Analysis ----------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the StackMap Liveness analysis pass. The pass calculates
11 // the liveness for each basic block in a function and attaches the register
12 // live-out information to a stackmap or patchpoint intrinsic if present.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "llvm/ADT/Statistic.h"
17 #include "llvm/CodeGen/LivePhysRegs.h"
18 #include "llvm/CodeGen/MachineFrameInfo.h"
19 #include "llvm/CodeGen/MachineFunction.h"
20 #include "llvm/CodeGen/MachineFunctionAnalysis.h"
21 #include "llvm/CodeGen/MachineFunctionPass.h"
22 #include "llvm/CodeGen/Passes.h"
23 #include "llvm/Support/CommandLine.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Support/raw_ostream.h"
26 #include "llvm/Target/TargetSubtargetInfo.h"
27 
28 using namespace llvm;
29 
30 #define DEBUG_TYPE "stackmaps"
31 
32 static cl::opt<bool> EnablePatchPointLiveness(
33     "enable-patchpoint-liveness", cl::Hidden, cl::init(true),
34     cl::desc("Enable PatchPoint Liveness Analysis Pass"));
35 
36 STATISTIC(NumStackMapFuncVisited, "Number of functions visited");
37 STATISTIC(NumStackMapFuncSkipped, "Number of functions skipped");
38 STATISTIC(NumBBsVisited,          "Number of basic blocks visited");
39 STATISTIC(NumBBsHaveNoStackmap,   "Number of basic blocks with no stackmap");
40 STATISTIC(NumStackMaps,           "Number of StackMaps visited");
41 
42 namespace {
43 /// \brief This pass calculates the liveness information for each basic block in
44 /// a function and attaches the register live-out information to a patchpoint
45 /// intrinsic if present.
46 ///
47 /// This pass can be disabled via the -enable-patchpoint-liveness=false flag.
48 /// The pass skips functions that don't have any patchpoint intrinsics. The
49 /// information provided by this pass is optional and not required by the
50 /// aformentioned intrinsic to function.
51 class StackMapLiveness : public MachineFunctionPass {
52   MachineFunction *MF;
53   const TargetRegisterInfo *TRI;
54   LivePhysRegs LiveRegs;
55 
56 public:
57   static char ID;
58 
59   /// \brief Default construct and initialize the pass.
60   StackMapLiveness();
61 
62   /// \brief Tell the pass manager which passes we depend on and what
63   /// information we preserve.
64   void getAnalysisUsage(AnalysisUsage &AU) const override;
65 
66   /// \brief Calculate the liveness information for the given machine function.
67   bool runOnMachineFunction(MachineFunction &MF) override;
68 
69 private:
70   /// \brief Performs the actual liveness calculation for the function.
71   bool calculateLiveness();
72 
73   /// \brief Add the current register live set to the instruction.
74   void addLiveOutSetToMI(MachineInstr &MI);
75 
76   /// \brief Create a register mask and initialize it with the registers from
77   /// the register live set.
78   uint32_t *createRegisterMask() const;
79 };
80 } // namespace
81 
82 char StackMapLiveness::ID = 0;
83 char &llvm::StackMapLivenessID = StackMapLiveness::ID;
84 INITIALIZE_PASS(StackMapLiveness, "stackmap-liveness",
85                 "StackMap Liveness Analysis", false, false)
86 
87 /// Default construct and initialize the pass.
88 StackMapLiveness::StackMapLiveness() : MachineFunctionPass(ID) {
89   initializeStackMapLivenessPass(*PassRegistry::getPassRegistry());
90 }
91 
92 /// Tell the pass manager which passes we depend on and what information we
93 /// preserve.
94 void StackMapLiveness::getAnalysisUsage(AnalysisUsage &AU) const {
95   // We preserve all information.
96   AU.setPreservesAll();
97   AU.setPreservesCFG();
98   // Default dependencie for all MachineFunction passes.
99   AU.addRequired<MachineFunctionAnalysis>();
100 }
101 
102 /// Calculate the liveness information for the given machine function.
103 bool StackMapLiveness::runOnMachineFunction(MachineFunction &MF) {
104   if (!EnablePatchPointLiveness)
105     return false;
106 
107   DEBUG(dbgs() << "********** COMPUTING STACKMAP LIVENESS: " << MF.getName()
108                << " **********\n");
109   this->MF = &MF;
110   TRI = MF.getSubtarget().getRegisterInfo();
111   ++NumStackMapFuncVisited;
112 
113   // Skip this function if there are no patchpoints to process.
114   if (!MF.getFrameInfo()->hasPatchPoint()) {
115     ++NumStackMapFuncSkipped;
116     return false;
117   }
118   return calculateLiveness();
119 }
120 
121 /// Performs the actual liveness calculation for the function.
122 bool StackMapLiveness::calculateLiveness() {
123   bool HasChanged = false;
124   // For all basic blocks in the function.
125   for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
126        MBBI != MBBE; ++MBBI) {
127     DEBUG(dbgs() << "****** BB " << MBBI->getName() << " ******\n");
128     LiveRegs.init(TRI);
129     LiveRegs.addLiveOuts(MBBI);
130     bool HasStackMap = false;
131     // Reverse iterate over all instructions and add the current live register
132     // set to an instruction if we encounter a patchpoint instruction.
133     for (MachineBasicBlock::reverse_iterator I = MBBI->rbegin(),
134          E = MBBI->rend(); I != E; ++I) {
135       if (I->getOpcode() == TargetOpcode::PATCHPOINT) {
136         addLiveOutSetToMI(*I);
137         HasChanged = true;
138         HasStackMap = true;
139         ++NumStackMaps;
140       }
141       DEBUG(dbgs() << "   " << LiveRegs << "   " << *I);
142       LiveRegs.stepBackward(*I);
143     }
144     ++NumBBsVisited;
145     if (!HasStackMap)
146       ++NumBBsHaveNoStackmap;
147   }
148   return HasChanged;
149 }
150 
151 /// Add the current register live set to the instruction.
152 void StackMapLiveness::addLiveOutSetToMI(MachineInstr &MI) {
153   uint32_t *Mask = createRegisterMask();
154   MachineOperand MO = MachineOperand::CreateRegLiveOut(Mask);
155   MI.addOperand(*MF, MO);
156 }
157 
158 /// Create a register mask and initialize it with the registers from the
159 /// register live set.
160 uint32_t *StackMapLiveness::createRegisterMask() const {
161   // The mask is owned and cleaned up by the Machine Function.
162   uint32_t *Mask = MF->allocateRegisterMask(TRI->getNumRegs());
163   for (LivePhysRegs::const_iterator RI = LiveRegs.begin(), RE = LiveRegs.end();
164        RI != RE; ++RI)
165     Mask[*RI / 32] |= 1U << (*RI % 32);
166 
167   TRI->adjustStackMapLiveOutMask(Mask);
168   return Mask;
169 }
170